(1) Field of the Invention
This invention relates to a butterfly valve comprising a valve housing having tubular portions, a valve stem extending in the tubular portions and carrying a valve closure member rotatable in the valve housing, gland packing portions provided between the stem and the tubular portions to prevent fluid leakage, and bearing portions for the valve stem provided outwardly of the gland packing portions respectively.
(2) Description of the Prior Art
This type of butterfly valve is suitable for use on a pipeline for transmitting high temperature and high pressure fluid such as exhaust gas resulting from combustion, and generally has bearing portions for the valve stem disposed outwardly of gland packing portions to avoid sticking due to the heat of the fluid. Since the bearing portions are far apart, the valve stem flexes a great deal under the fluid pressure acting on the valve closure member when the valve is completely closed, which results in bad sealing. It has been proposed to provide a large diameter stem to reduce the flexion, but this has a disadvantage of leaving a small opening area when the valve is fully open and deteriorating flow characteristic.